1. Field of the Invention
The present invention relates to a valve opening and closing mechanism in engines. In particular, the present invention relates to the valve opening and closing mechanism in engines which does not require any adjustment work of tappet clearances.
2. Prior Art
In automotive engines, as shown in FIG. 1, there are provided with rocker arms 2 and 3 which are actuated by means of cams 1. The rocker arms 2 and 3 are provided with through holes at each one end and through which push rods 5, 5 are inserted, respectively. The rocker arms 2 and 3 rock consecutively as the cams 1 rotate.
For instance, when the push rod 5 in gas exhaust side advances, a valve stem 11 moves downward against the force of a valve spring 12 to open a valve 10. Whereas, when the push rod 5 returns backward, the valve stem 11 moves upward by means of the force of the valve spring 12 to close the valve 10. This construction of the valve mechanism is substantially same in gas intake side consisting of a valve 20, a valve stem 21 and a valve spring 22.
In practical operation of engines, the valve 10 of this valve opening and closing mechanism is expanded due to the heat generated in actual operation of engines. As shown in FIG. 2A, when the valve 10 is heat expanded, the lower end of said valve 10 moves downward by contacting the head of the valve stem 11 with the lower end portion of the push rod 5 in the rocker arm 3 and, as shown in FIG. 2B, a clearance B is generated between the valve 10 and a combustion chamber 30. The gas in the combustion chamber 30 is thus leaked to disturb satisfactory operation of engines.
In order to avoid such unfavorable condition, a tappet clearance TC is formed between the valve 10 and the push rod 5 in conventional engines. This is shown in FIG. 1B. When the valve 10 is heat expanded in actual operation of engines and a displacement due to such heat expansion is generated, it is absorbed by means of the tappet clearance TC.
Practically, when engines are assembled, an adjustment screw 41 is rotated by means of a screwdriver 42 so that a predetermined clearance of TC between the valve 10 and the push rod 5 may be attained. This adjustment work of the tappet clearance TC is achieved by a workman. Various thickness gauges and some differential.pressure gauges are applied for the adjustment work (not shown in FIG. 1B).
However, there have been observed some defects in the adjustment work of the conventional tappet clearance TC. It always needs an extra workman to adjust the tappet clearance. There also have been observed some adjustment errors or unintentional disregarding of adjustment work. As thickness gauges are used by workman, an accurate adjustment cannot be expected. The adjustment work also requires long time.
Further, due to an existence of the tappet clearance TC, the push rod 5 hits the valve stem 11 when said valve 10 is pressed to be opened. In this occasion, the tappet noises are generated. This is also a problem inevitable.
Apart from the aforementioned tappet clearance adjustment work there has been a system called an oil tappet. This system applies a hydraulic pressure to automatically adjust tappet clearances. However, such oil tappet system requires some liquid passages. Arrangement of the liquid passages is rather complex. It is, therefore, difficult to apply said system to applicant's HONDA V-TEC engine.
The object of the present invention is to offer a valve opening and closing mechanism which is easy to be applied to somewhat complex engines like the HONDA V-TEC engine. The valve opening and closing mechanism according to the present invention does not require any adjustment work of tappet clearances. A clearance between the push rod and the valve is eliminated. Unfavorable effects due to the adjustment work by workman are eliminated.